FIGS. 21 and 22 show a conventional transmission guide 800 for use in the timing transmission of an automobile engine. The guide comprises a shoe 810 having a sliding contact surface 810a on which a transmission chain C slides, and a separately molded base 820 for supporting, and maintaining the configuration of, the shoe 810. The shoe 810 is formed with hooks 813, which can be provided on both sides of the shoe 810, and the base 820 is cut away to form hook-receiving notches 823. The shoe 810 and the base 820 are assembled by twisting the shoe, and engaging the hooks 813 with the notches 813, as described in United States Patent Application Publication No. 2005/0079938, dated Apr. 14, 2005.
In another known chain guide, disclosed in laid-open Japanese Patent Application No. 2004-150615, dated May 27, 2004, the back surface of a synthetic resin shoe is fused to the front surface of a base composed of another synthetic resin.
In the operation of the transmission guide 800 in FIGS. 21 and 22, if the side wall 811 of the shoe 810 is low, i.e., it does not extend far enough from the sliding-contact surface 810a, the transmission chain can straddle and ride over the side wall 811, and damage parts of the transmission.
If an external force is applied to the side wall 811 of a shoe 810 having a low rigidity compared to that of the base 820, the side wall 811 can bend inward in the direction of the width of the guide, and the edge of the side wall 811 may contact, and hamper the travel of, the transmission chain.
Furthermore, if the transmission chain vibrates due to load variations as it travels on the sliding contact surface, the shoe 810 can move longitudinally by an amount corresponding to the clearance allowed for installation of the hooks in the hook-receiving notches. Therefore, a hook 812 of the shoe 810 can locally abut a notch 823 of the base 820 causing an excessive concentration of stress which can cause breakage of the hook, a change in the relationship between the shoe and the base, and result in destabilization of the path of the transmission chain.
On the other hand, in the case of the chain guide of laid-open Japanese Patent Application No. 2004-150615, the strength of the fused connection between the shoe and the base cannot be maintained over a long time, and, when the transmission chain becomes located eccentrically in the direction of the width of the guide, and a shear force acts on the shoe in the direction of the width of the guide, the shoe can become detached from the base.